July 2004

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PHILADELPHIA, PA - Experimental work by researchers at Brookhaven National Laboratory indicate that catalysts employing metals other than platinum may be possible, participants in the U.S. Energy Department’s annual Hydrogen Program Review here were told.

A paper by principal investigator Radoslav Adzic and four collaborators on “Low Platinum Loading Catalysts” was described by one expert as one of the “most exciting” highlights of the three-day session May 24-27 here. Some 170 papers in seven different categories - fuel cells, education, production and delivery, safety, storage, technical validation plus the plenary session - were presented to the more than 500 researchers, experts, executives and government officials who attended the meeting.

The team’s basic approach was to develop low-platinum-loading electrocatalysts by placing a submonolayer-to-submonolayer pf platinum on nanoparticles of suitable metals or alloys to either ultimately reduce platinum loading, enhance the noble metals catalytic activity or completely utilize the metal’s catalytic capabilities.

Citing experimental results from Los Alamos National Laboratory, Adzic said on the anode side, catalysts with 18 µg platinum/cm2 plus ruthenium showed no voltage loss after 770 hours and small losses for longer runs. He said the DoE durability target of 2000 hours for next year can be reached with this catalyst. Put another way, the DoE target of 0.6 g/kW is met for platinum; in fact, ”only 0.063 g Pt/kW is necessary,” his slide said. If the ruthenium is counted, a total of 0.630 grams of metal is needed.

On the cathode side, Adzic reported a platinum monolayer on carbon-supported metal or metal alloy nanoparticles “can be an active catalyst for O2 reduction.” He also reported that a palladium/cobalt/carbon electrocatalyst has been synthesized whose “activity is comparable” to that of platinum, as has been another catalyst composed of platinum, gold, nickel and carbon.

The significance of these findings, noted one participant, was that in the past, the consensus had been that only platinum had the electronic structure needed for catalysis. Now, it appears that cadmium/palladium materials mimic this behavior. However, the participant observed, cadmium/platinum catalysts will be unstable in the acidic environment of a fuel cell. Nevertheless, this line of research investigating non-platinum catalysts is regarded as “most promising.”

“Grape” -Structured Nanocatalysts

New catalyst materials was also the subject of a paper by Lawrence Berkeley National Laboratory researcher Philip N. Ross, Jr., aided by staff scientist Nenad M. Markovic, a post doctoral fellow and two graduate students. The team is investigating the design of new catalysts for anodes and cathodes in a unified concept based on bi-metallic nanoparticles with a “grape” structure: a “skin” consisting of a metal from the platinum group surrounding a core consisting of a base metal.

The group is pursuing new synthetic chemistry to produce nanoparticles of this type, focussing on rhenium as metal core with platinum and palladium as skin material. The team is also investigating optimization of gold/palladium alloys as an alternative to platinum in anodes. “Great fundamental studies,” was one comment. “Progress this year seems most significant,” and it’s the “only group really characterizing catalyst structure at the atomic scale.”

Los Alamos 20W DFC Stack Debuts in Military Test

A paper by a 13-member Los Alamos National Laboratory team headed by Piotr Zelenay on direct methanol fuel cells (DMFCs), focused on catalyst r&d, membranes and membrane-electrode assemblies, and DFC stacks and sensors.

Among other things, the team reported Los Alamos DFC stacks and sensors had been integrated by Ball Aerospace into first demonstration units for the military, the Defense Advanced Research Projects Agency (DARPA). Rated power is 20 W at 12V, the specific power for a 72 hour mission is 500 W/kg, efficiency is 33%, and the energy yield from fuel is 2 kWh/kg, “respectable specific power & system efficiency,” one of the team’s slides said.

The team also reported on methods for synthesizing and demonstrating a new unsupported DFC cathode catalyst. The new material, said a slide, reduced average particle size by at least 40% - from 6 nm (Johnson Matthey’s HiSPEC 1000, the state-of-the-art Pt black catalyst for DMFCs, according to the paper) to 3.6 nm and 4.8 nm for Pt black and Pt/SiO2, respectively - and performance superior to the best commercial cathode catalysts.

The presentation demonstrated “good integration of catalyst-membrane-MEA work,” said the observer. It continues the group’s “tradition of identifying the core problem and providing a solution that achieves milestones. You can’t argue with success.”

Other papers regarded by experts as significant:

– “Microstructural characterization of PEM Fuel Cells,” led by Karen More of Oak Ridge National Laboratory in collaboration with two other ORNL colleagues and one from Los Alamos National Laboratory, reported on efforts to understand degradation mechanisms in MEAs and morphological changes occurring during MEA aging and use. The authors collaborated with PEM developers and manufacturers to evaluate MEAs using advanced microstructural characterization techniques and provide feedback for MEA optimization.

A review participant called it “the best technical advancement of the meeting,” adding the results are “critical to understanding” these processes, producing “deep understanding” of MEA microstructure.

– A paper by a 3M researcher, Mark K. Debe, on “Advanced MEAs for Enhanced Operating Conditions, Amenable to High Volume Manufacture,” was also regarded as valuable. Debe described work on durable, lower cost next-generation thin-film MEAs with ultra-thin layer catalyst electrodes operating in the range of 85 to more than 120 deg. C temperatures that could utilize roll-good fabrication processes to achieve lower cost.

Debe’s second area of work is the development of MEAs operating at even higher temperatures, in the 120-150 deg. C-plus area that do not rely on standard modes of aqueous proton conduction. Debe’s research attempts to understand the relationship between materials, proton conductivity, temperature and other factors, involving the screening of materials and fabrication processes.

3M has been working with several universities and two national laboratories on this project. Progress in both catalyst and membrane development was judged as “very significant” producing “several valuable achievements,” and the project is rated as an example of “good team university/national lab collaboration.”

- Another industry paper, “Enabling Commercial PEM Fuel Cells With Breakthrough Lifetime Improvements,” by Jayson W. Bauman of DuPont, was also well received. In this program, DuPont has developed an understanding of potential mechanisms that can lead to membrane failure and has developed strategies involving base polymer improvements, chemical stabilization, membrane reinforcement and MEA and UEA design to extend MEA lifetimes.

DuPont has teamed with UTC Fuel Cells and the United Technologies Research Center to form a core team that has been investigating MEA durability improvements for three years. The University of Connecticut Global Fuel Cell Center (H&FCL Jan. 04) is now also part of that core group. In a new program that is still in its first year, the research group has demonstrated feasibility of several durability improvement strategies. Work planned between now and the program’s end in September 2006 includes material synthesis, accelerated aging testing and stack testing, analysis and modeling, materials characterization and analysis and cost analysis. The goal is a membrane completely resistant to chemical attack, with increased tensile strength and other improvements.

The paper presented a good combination of MEA structure and material development, commented an observer, displayed significant progress on resistance to peroxide attacks, and a good team had been assembled to go from raw materials all the way to full power plants. Source: the papers can be downloaded in PDF from DoE’s EERE site: www.eere.energy.gov/hydrogenandfuelcells/
2004_annual_review.html.